Circuit interruption devices generally include a pair of mechanical switching contacts connected between a source of power and the controlled circuit which rapidly become separated by means of an operating mechanism upon command. When the contacts become separated, an arc is formed therebetween which continues to carry current until the current ceases. Since the energy associated with the arc can seriously damage the contacts, it is expedient to stop the current flow as rapidly as possible. The state of the art is resplendent with various arc chamber configurations and materials which are structured to rapidly increase arc voltage. Earlier attempts have been made to provide an "arcless" circuit interrupter wherein semiconductor elements are employed in various combinations with the switching contacts to reduce the effects of arcing. U.S. Pat. No. 3,558,910 to Robert G. Dale, for example, describes a bilateral semiconductor switch connected in parallel with the contacts of an electromechanical relay to prevent contact arcing. U.S. Pat. No. 3,543,047 to Robert M. Renfrew describes a two switch arrangement in series with a low voltage electrical power source and a load. A varistor shunt across one of the switches absorbs the energy to be interrupted when the switch is opened and attenuates the current to reduce the arcing when the other switch is later opened.
U.S. Pat. No. 4,420,784 to Chen et al., entitled "Hybrid DC Power Controller", describes a field effect transistor and a Zener diode between a pair of separable power contacts. An arc chute is required to control the arc that forms across the contacts to increase the arc voltage to reduce the let-through fault current through the contacts.
The purpose of this invention is to provide a solid state switch in parallel with a pair of contacts to first, after opening the contacts, transfer the current from the contacts through the solid state switch at a low voltage drop to extinguish the arc that forms momentarily between the contacts and then to increase the voltage drop in the absence of an arc so that the current then rapidly drops to zero.